410 Gonthier and Nicolotti: Identifying Common Wood Decay Fungal Species Arboriculture & Urban Forestry 2007. 33(6):410–420. A Field Key to Identify Common Wood Decay Fungal Species on Standing Trees Paolo Gonthier and Giovanni Nicolotti Abstract. A field key to species is presented for the most important and widespread European wood-rotting basidiomycetes on standing trees. Sixty-four fungal taxa belonging to 36 genera and 17 families of Agaricales, Hymenochaetales, Polypo- rales, and Russulales are included in the key, which was mostly based on macroscopic features of the basidiomata. The key was validated in the field and allowed for easy recognition of wood decay fungi. Key Words. Basidiocarp; basidiomata; diagnosis; field guide; simplified key. Wood decay fungi are the primary biotic decomposers of wood. In forest ecosystems, they play an important role in carbon and nitrogen cycling and help to convert organic de- bris into the humus layer of the soil. They colonize downed timber and slash on the forest floor, lumber, and even wood in service. Wood decay fungi can also attack living trees, acting either as true pathogens responsible for root rots and stem cankers or as rotting agents of heartwood and sapwood. Wood decay is a major source of loss in both timber produc- tion and wood use, and, importantly for landscape trees, in parks and urban forests, it can cause a tree to be hazardous (Butin 1995). With the exception of a few ascomycetes (e.g., Ustulina, Xylaria, Chaetomium), all the wood-attacking fungi are ba- sidiomycetes primarily belonging to Agaricales, Hymeno- chaetales, Polyporales, and Russulales (Kirk et al. 2001). Di- chotomous keys to species are available for lignicolous Eu- ropean Aphyllophorales (Breitenbach and Kränzlin 1986), an obsolete taxon that included genera from all the four previ- ously mentioned orders, or for specific groups within Aphyl- lophorales. For instance, analytical keys were built for Cor- ticiaceae s.l. (Hjortstam et al. 1978) and Polyporaceae s.l. (Bernicchia 2005). All these keys are based on the macro- morphology of the basidioma and the hymenophore and, es- pecially, on the hyphal system and on the micromorphology of septa, spores, basidia, cystidia, and other sterile organs. The assessment of the amyloidity or dextrinoidity of hyphae, spores, and hymenial organs through microscopic observa- tions of the staining reactions to Melzer’s solution is also needed for determination. Thus, regular identification of wood decay fungi requires specialized mycologists and equipped laboratories, and the identification can be rarely achieved in the field. ©2007 International Society of Arboriculture Identification keys to polypores are available on the Inter- net (Ryvarden 1998) or in computerized format (Adaskaveg et al. 1994). Furthermore, descriptions of wood-rotting fungi on standing trees, often equipped with simplified keys, are provided with practical field guides to urban tree pathology or to tree hazard assessment (Strouts and Winter 1994; Lonsdale 1999; Intini et al. 2000). These simplified keys, however, are based also on ecological characters such as host preference, which is questionable considering that only few wood decay fungi display high levels of host specialization (Rayner and Boddy 1988; Nicolotti et al. 2004a). Moreover, simplified keys only go to the genera level or they allow for the dis- crimination of groups of genera (Lonsdale 1999; Alaux 2006). There is good reason, especially in tree hazard assess- ment, to make accurate identification at the species level of the fungi concerned, because the behavior of wood-rotting fungi in terms of aggressiveness and ability to overcome host defenses can be highly variable among different species within genera (Schwarze and Baum 2000). This could aid in prognosis if the typical patterns of spread within the tree and the effects on wood strength of fungal species are known and, therefore, to some extent predictable (Lonsdale 1999). A field key to species, based on the macroscopic features of basidiomata, is provided for the identification of the most important and widespread European wood-rotting basidiomy- cetes on standing trees. MATERIALS AND METHODS European wood-rotting species of basidiomycetes were se- lected to be included in the key based on their frequency of occurrence on standing trees as determined from previously published information (Breitenbach and Kränzlin 1986; Nico- lotti et al. 2004a; Bernicchia 2005). In addition to widespread
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